org.apache.commons.collections4.map
Class LazyMap<K,V>

java.lang.Object
  extended by org.apache.commons.collections4.map.AbstractIterableMap<K,V>
      extended by org.apache.commons.collections4.map.AbstractMapDecorator<K,V>
          extended by org.apache.commons.collections4.map.LazyMap<K,V>
All Implemented Interfaces:
Serializable, Map<K,V>, Get<K,V>, IterableGet<K,V>, IterableMap<K,V>, Put<K,V>
Direct Known Subclasses:
LazySortedMap

public class LazyMap<K,V>
extends AbstractMapDecorator<K,V>
implements Map<K,V>, Serializable

Decorates another Map to create objects in the map on demand.

When the get(Object) method is called with a key that does not exist in the map, the factory is used to create the object. The created object will be added to the map using the requested key.

For instance:

 Factory<Date> factory = new Factory<Date>() {
     public Date create() {
         return new Date();
     }
 }
 Map<String, Date> lazy = LazyMap.lazyMap(new HashMap<String, Date>(), factory);
 Date date = lazy.get("NOW");
 
After the above code is executed, date will refer to a new Date instance. Furthermore, that Date instance is mapped to the "NOW" key in the map.

Note that LazyMap is not synchronized and is not thread-safe. If you wish to use this map from multiple threads concurrently, you must use appropriate synchronization. The simplest approach is to wrap this map using Collections.synchronizedMap(Map). This class may throw exceptions when accessed by concurrent threads without synchronization.

This class is Serializable from Commons Collections 3.1.

Since:
3.0
Version:
$Id: LazyMap.java 1479407 2013-05-05 22:07:53Z tn $
See Also:
Serialized Form

Nested Class Summary
 
Nested classes/interfaces inherited from interface java.util.Map
Map.Entry<K,V>
 
Field Summary
protected  Transformer<? super K,? extends V> factory
          The factory to use to construct elements
 
Constructor Summary
protected LazyMap(Map<K,V> map, Factory<? extends V> factory)
          Constructor that wraps (not copies).
protected LazyMap(Map<K,V> map, Transformer<? super K,? extends V> factory)
          Constructor that wraps (not copies).
 
Method Summary
 V get(Object key)
           
static
<K,V> LazyMap<K,V>
lazyMap(Map<K,V> map, Factory<? extends V> factory)
          Factory method to create a lazily instantiated map.
static
<V,K> LazyMap<K,V>
lazyMap(Map<K,V> map, Transformer<? super K,? extends V> factory)
          Factory method to create a lazily instantiated map.
 
Methods inherited from class org.apache.commons.collections4.map.AbstractMapDecorator
clear, containsKey, containsValue, decorated, entrySet, equals, hashCode, isEmpty, keySet, put, putAll, remove, size, toString, values
 
Methods inherited from class org.apache.commons.collections4.map.AbstractIterableMap
mapIterator
 
Methods inherited from class java.lang.Object
clone, finalize, getClass, notify, notifyAll, wait, wait, wait
 
Methods inherited from interface java.util.Map
clear, containsKey, containsValue, entrySet, equals, hashCode, isEmpty, keySet, put, putAll, remove, size, values
 

Field Detail

factory

protected final Transformer<? super K,? extends V> factory
The factory to use to construct elements

Constructor Detail

LazyMap

protected LazyMap(Map<K,V> map,
                  Factory<? extends V> factory)
Constructor that wraps (not copies).

Parameters:
map - the map to decorate, must not be null
factory - the factory to use, must not be null
Throws:
IllegalArgumentException - if map or factory is null

LazyMap

protected LazyMap(Map<K,V> map,
                  Transformer<? super K,? extends V> factory)
Constructor that wraps (not copies).

Parameters:
map - the map to decorate, must not be null
factory - the factory to use, must not be null
Throws:
IllegalArgumentException - if map or factory is null
Method Detail

lazyMap

public static <K,V> LazyMap<K,V> lazyMap(Map<K,V> map,
                                         Factory<? extends V> factory)
Factory method to create a lazily instantiated map.

Type Parameters:
K - the key type
V - the value type
Parameters:
map - the map to decorate, must not be null
factory - the factory to use, must not be null
Returns:
a new lazy map
Throws:
IllegalArgumentException - if map or factory is null
Since:
4.0

lazyMap

public static <V,K> LazyMap<K,V> lazyMap(Map<K,V> map,
                                         Transformer<? super K,? extends V> factory)
Factory method to create a lazily instantiated map.

Type Parameters:
K - the key type
V - the value type
Parameters:
map - the map to decorate, must not be null
factory - the factory to use, must not be null
Returns:
a new lazy map
Throws:
IllegalArgumentException - if map or factory is null
Since:
4.0

get

public V get(Object key)
Specified by:
get in interface Map<K,V>
Specified by:
get in interface Get<K,V>
Overrides:
get in class AbstractMapDecorator<K,V>
See Also:
Map.get(Object)


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